This invention relates to a device for and a method of processing the surface of a magnetic hard disk, its substrate and a semiconductor wafer.
Data processing devices for recording and reproducing data such as characters, images and sounds are coming to be incorporated not only into a personal computer but also into an electronic apparatus such as a television, a camera, a portable music player and a portable telephone. Such data processing devices are required to have a higher processing capability (or an increased recording capacity) and an improved accuracy in reproduction, as well as compactness.
Data processing devices record and reproduce such data magnetically by means of a magnetic head on and from a magnetic recording medium. The magnetic recording medium comprises an aluminum substrate having a Ni—P plating on its surface or a glass substrate (hereinafter generally referred to as the disk) with a substrate layer, a magnetic layer and a protective layer sequentially formed on its surface after it is subjected to polishing and texturing processes.
Methods of magnetically recording data on such a magnetic recording medium generally include the so-called longitudinal recording method for recording in the direction of the circumference and the perpendicular recording method for recording in the perpendicular directions.
According to the longitudinal recording method, the surface of the magnetic hard disk is made appropriately rough so as to prevent the magnetic head from becoming adsorbed thereonto and a magnetic layer is formed after a texturing process is carried out to form concentric circular marks on the disk surface for providing anisotropic magnetic characteristic to the magnetic layer in the direction of the circumference of the disk (substrate).
The texturing process is carried out for forming concentric circular marks on the surface of the disk by rotating the disk, supplying slurry to the disk surface, and oscillating a processing tape in the radial direction of the disk while pressing this processing tape through a contact roller. The rotational speed of the disk is within the range of 300 rpm or more and 600 rpm or less, the frequency of the oscillation is within the range of 5 Hz or more and 10 Hz or less, and the amplitude of the oscillation is about 1 mm.
The perpendicular recording method is for attaining an even higher recording density by orienting the magnetization axis of the magnetic layer (or the magnetic recording layer), which has been directed in a direction towards the interior of the magnetic recording medium, perpendicular to the surface of the magnetic recording medium. This method is now attracting attention as a new recording method taking the place of the longitudinal recording method.
The perpendicular magnetic recording medium is of a two-layer structure comprising a soft magnetic layer referred to as a soft magnetic backing layer (or a soft magnetic layer substrate layer) which is adapted to easily pass the magnetic fluxes from the magnetic head and is formed below a magnetic recording layer for recording data.
According to the perpendicular magnetic recording method, magnetic fields are not in the direction of the circumference, as done according to the longitudinal recording method described above. Instead, the surface of the disk must be processed such that magnetic fields are easily oriented in the perpendicular direction with respect to the surface of the disk. The soft magnetic backing layer is a layer for passing magnetic field such that the magnetic recording layer is magnetized in the perpendicular direction. Thus, methods of providing a magnetic anisotropy such that the magnetization axis of a soft magnetic layer will be oriented in the direction of the diameter of the disk are being investigated as technologies for improving recording and reproduction and obtaining superior recording and reproduction characteristics with low noise by improving the magnetic permeability in the circumferential direction of the soft magnetic layer, as described, for example, in Japanese Patent Publications Tokkai 6-180834, 10-214719 and 2-126421.
Japanese Patent Publications Tokkai 6-180834 and 10-214719 describe technology of forming a ferromagnetic layer of a Co alloy or the like as the upper or lower layer of the soft magnetic backing layer and magnetizing this layer in a desired direction and technology of forming a paramagnetic layer and pinning magnetization by using exchange bonding.
As a technology for providing magnetic anisotropy such that the magnetization axis of a soft magnetic layer will be oriented in the radial direction of the disk, Japanese Patent Publication Tokkai 2-126421 discloses a method of forming fine straight grooves in the radial direction on the surface of a disk such that the magnetization axis of the soft magnetic backing layer formed on the disk will be directed along these grooves and that the magnetic permeability of the soft magnetic backing layer will have high values in the circumferential direction of the magnetic recording medium.
Such straight grooves cannot be formed in the radial direction of a disk with a sufficiently high processing speed (or with a sufficiently high throughput), however, with conventional disk processing devices which have been used simply as a texturing device for the longitudinal recording method.
As shown, for example, in FIG. 8 of Japanese Patent Publication Tokkai 8-7266 and FIG. 7 of Japanese Patent Publication Tokkai 8-63745, disk processing devices used for the texturing are adapted to rotate a disk, to supply polishing slurry to its surface through a nozzle, to press a processing tape to it through a contact roller and to cause this processing tape to undergo a reciprocating motion (or to oscillate) in the radial direction of the disk such that concentric circular marks are formed on the disk surface, the rotational speed of the disk being within the range of 300 rpm or more and 600 rpm or less, the frequency of the oscillation being within the range of 5 Hz or more and 10 Hz or less, and the amplitude of the oscillation being about 1 mm, as explained above.
With such a conventional disk processing device, the oscillating motion is effected while the disk is rotated at a fixed position and causing the contact roller to undergo a reciprocating motion in the radial direction of the disk by means of a piezoelectric element, a linear motor or an eccentric cam.
If a piezoelectric element is used for the oscillation, a sufficiently large amplitude cannot be attained. The force for effecting the reciprocating motion varies, depending on the amplitude, and there is also the problem of poor durability.
If a linear motor is used for the oscillation, a sufficiently large amplitude can be attained but since it relies on magnetism, it is not suitable for the processing of a magnetic recording medium.
If an eccentric cam is used for the oscillation, the contract roller can be reciprocatingly moved with a sufficiently large amplitude, the amplitude can be controlled with a high level of accuracy and the frequency can be made large. If both the amplitude and the frequency are increased, however, the device begins to vibrate due to frictions, etc. of the mechanism for converting the rotation of the motor into the linear reciprocating motion of the contact roller, and hence the disk cannot be processed with a high level of accuracy. For this reason, it has been difficult to achieve an oscillation with frequency in excess of 20 Hz with a conventional technology. In other words, the rotational speed of the disk had to be lowered with a conventional disk processing device and a sufficiently large throughput could not be obtained.